Torque Control on componet at different temperatures

[wade75]

Greetings,

          I am in the process of building an application with Motion Control with change control modes from position control to Torque Control.  Here is my situation.  I am going to be twisting a rubber component from +- X Nm's at a particular frequency.  However the component will be under temperature extremes and as the component heats up and cools down the stiffness changes therefore it may take more or less angle to achieve programmed torque.  I still have to keep my frequency unchanged during the transition though.  Is there automatic error compensation for velocity to keep the frequency unchanged even though the distance required to achieve Torque setpoints will change?  I hope this is Clear enough to get a handle on what I am trying to achieve.  I have no problem with Position Control, it is essentially the Torque Control frequency compensation that is what I need advice on.

Regards,

        Wade

[Jochen]

Wade,

for this purpose you will have to change the feedback for your motor to a signal that is proportional to torque. One option is to use a torque sensor with an analog output signal in the range of +/- 5 V or +/- 10 V. You can use an NI-Motion control device in analog feedback mode then and instead of defining a position profile you could define a torque profile then (e. g. by using contouring mode). With such a setup the motor will travel as far as it is needed to generate the torque profile, regardless of the travel distance.

To learn more about analog feedback, please have a look at this thread.

Regards,

Jochen

[wade75]

Jochen,

         Thanks for the reply.  Right now I have it setup for a sequence of blending moves to accomplish the cycle.  I am using analog feedback as the control method.  This way I can monitor the blending moments to keep track of cycles.  By Contouring would the velocity be changed automatically to reach the torque setpoints at a predifined frequency, even with the amout of distance increasing or decreasing?

Wade

[Jochen]

Wade,

the behavior of blended moves doesn't differ so much from the behavior of contoured moves. The main difference is the fact, that with contouring you can define position or torque profiles with a better resolution, as everything is executed onboard and you don't have to send blend-commands inbetween the moves. Still you can monitor the number of cycles as you actively refill the contouring buffer in your host application.

So the answer to your question is yes. With analog feedback position and velocity doesn't play a role. In your case in contouring mode you can define the torque profile (torque vs. time) directly and the motion control board adjusts travel distance and velocity accordingly.

Jochen

[wade75]

Thanks Jochen,  Sounds like countouring is the way to go.